As methods for synthesizing a polyamino acid, conventional methods using chemical synthesis, enzymatic synthesis or the like are known.
Recently, various bioactive peptides realizing high degree of social contribution have been found. Examples of methods for synthesizing such peptides include the chemical synthesis method and the enzymatic synthesis method. Using the latter method, peptides can be produced without any harmful chemicals, and problems of environmental burden, etc. can be overcome. In addition, cost reduction can also be expected.
As one of methods for enzymatically synthesizing a polyamino acid, a method for enzymatically synthesizing a nonprotein amino acid polymer consisting of an aspartic acid backbone and arginine side chains, cyanophycin (multi-L-arginyl-poly(L-aspartic acid)) is known (Non-patent documents 1 and 2). A method for enzymatically synthesizing poly-γ-glutamic acid has also been reported (Non-patent document 3).
However, since enzymatic synthesis of these polyamino acids is accomplished by the catalyst action of a multiple-enzyme system, it is difficult to control, and therefore it has not been applied to industrial production. Further, except for the cases of the enzymatic synthesis of cyanophycin and poly-γ-glutamic acid, there is no example of a peptide having a long chain (equal to or longer than a tripeptide) or amino acid homopolymer successfully synthesized enzymatically.
Regarding biosynthesis of an antibacterial polyamino acid ε-poly-L-lysine, biosynthesis using the microbial fermentation method has been reported (Non-patent document 4).
[Non-patent document 1] Eur. J. Biochem. 267, 5561-5570 (2000)
[Non-patent document 2] APPL. ENVIRON. MICROBIOL. Vol. 67, No. 5, May 2001, pp. 2176-2182
[Non-patent document 3] APPL. ENVIRON. MICROBIOL. Vol. 70, No. 7, July 2004, pp. 4249-4255
[Non-patent document 4] Agric. Biol. Chem. Vol. 45, 1981, pp. 2497-2502